The objectives of this project are to use samples and existing data from the Women's Health Initiative Memory Study (WHIMS;n=7152) to determine the relations between RBC omega-3 fatty acid (FA) content and measures of cognitive function. Our hypothesis is that these are inversely associated. The existence of two sub-studies within the WHIMS cohort, the'WHI Study of Cognitive Aging and the WHIMS Magnetic Resonance Imaging, make it possible to assess cognitive function in a variety of ways: clinically, with formal cognitive testing, and by brain anatomy. Relations of RBC FA patterns with the latter wil be examined only cross sectionally, but with the former two endpoints, relations wil be assessed both cross sectionally and prospectively. Finally, since WHIMS contained two placebo-controlled, randomized trials of hormone treatment, we will test the hypothesis that estrogen stimulates the synthesis of omega-3 FAs from short-chain dietary precursors (alpha-linolenic acid) and thereby raises RBC levels of the long-chain omega-3 FAs, eicosapentaenoic and docosahexaenoic acids.